Thanks for the clarification (although it's not a hansen board, it's on some copper-pad protoboard). I'm not using any pots, BTW.
However, I did some Tier 1 ("Do you need stamps to send e-mail"-type) troubleshooting, and found that most of the hiss vanishes when I connect it to my McIntosh instead of my computer (because I have a MAJOR jumble of cables behind my computer, and the sum total of all the electrical noise is probably totally random). However, there IS some *very* quiet, backround white noise which is barely audible when I move the (unshielded) amp away from the source of AC hum known as my audio setup.
However, it seems to suffer from some hum when connected properly (wired into the amp with its grounded phono plug), which I assume is due to the wires that connect some components, and not a soldering mishap.
So, in the end, it turns out the problem is probably not with my amp anyway. Well, I sure learned a lot